Electrolyte analyzer

ABSTRACT

A reagent and wash fluid supply system for a flow through analyzing system which includes a tubular fluid sampling probe (70), having a sampling port (63) which aspirates air, sample and liquid reagents through the analyzing system which cooperates with a slide valve (64) having a passageway (53) through which the probe reciprocates. The passageway contains a plurality of chamber ports (46, 47, 48) each of which is sealed from the other ports by the tube sampling probe when its sampling port is positioned within a chamber port. A reagent pouch having a plurality of chambers communicating with a separate chamber port in the slide valve (20, 21) contains liquid reagents and a wash solution. One chamber in the reagent pouch receives waste.

DESCRIPTION Field of the Invention

This invention relates to stat analyzers which determine the activity ofelectrolytes in solutions, and in particular, biological fluids.

BACKGROUND OF THE INVENTION

The first automated analyzers utilizing ion selective electrodes formeasuring electrolytes in whole blood, plasma, or serum were developedin 1975 by Orion Research Incorporated. Orion's model SS-30 measuredpotassium and sodium, and its model SS-20 measured ionized calcium.Since that time, other analysers have been developed by Corning, Model902; Instrumentation Laboratory, Models 501, 502, and 504, which aredescribed in U.S. Pat. No. 4,283,262 granted Aug. 11, 1981, to Cormieret al. and U.S. Pat. No. 4,304,257, granted Dec. 8, 1981, to Webster;Nova Biomedical Corporation, Nova 1, 4, and 5; Kone OY, Microlyte;Radiometer, Model KNAI; Guilford Chemlyte NA/K; Beckman, Electrolyte 2and System F4A; AVL Model 980; Dow Corning Direction 6000; Worthington,IE8200; and Photovolt 4M.

A most recent and advanced unit in the art is Orion's Model 1020. Itdoes, however, have some limitations. First, it has separate bottles forits standardizing and maintenance solutions as well as a bottle tocollect spent reagents and sample solutions. The operator is required toplace different tubes in each bottle, and to change the bottles atdifferent times. Orion's earlier model SS-30 utilized a cardboard fluidspack containing individual laminate reagent pouches and a plasticdisposal bag into which separate plastic tubes were placed. Secondly,the Model 1020 requires manual operator interactive calibrationprocedures to adjust pumping to compensate for physical change in theperistaltic pump tubing. A third limitation is an expensive carriageassembly containing the ion selective electrodes, reservoir housing, andsample probe, all which have to be moved up and down when the analyzeraspirates a sample. The present invention overcomes these limitations.

The principal object of the invention is to provide a mechanicallysimple, low cost, user friendly, fully automated, electrolyte analyzer.

Another object is to provide an electrolyte analyzer with continuous andautomatic pump tubing calibration.

Another object of the invention is to provide a stat electrolyteanalyzer with a unique and automatic detection system for sensingbubbles or air segments, and for determining sample and reagentposition.

Yet another object is to provide an electrolyte analyzer having anintegrated reagent and waste disposal system.

SUMMARY OF THE INVENTION

The invention resides in an analyzer for measuring the ionic values ofelectrolytes in a sample solution and includes a fluid flow-through airsegment detector and in a plurality of fluid flow-through ion selectiveelectrodes for measuring the ionic values of electrolytes and in a fluidflow-through reference membrane assembly connected in series. Alsoincluded is a reference electrode and a reservoir containing an internalfilling solution. The reference membrane assembly and the referenceelectrode are located in the reservoir and are exposed to the internalfilling solution.

The analyzer includes a tubular fluid sampling probe which has one endclosed and a sampling port spaced a finite distance from the closed end.The other end of the probe is in fluid communication with the airsegment detector. The tubular fluid sampling probe cooperates with aslide valve which has a passageway in which the tube reciprocates. Thepassageway contains a plurality of chamber ports each of which is sealedfrom the other ports by the sampling probe when the sampling port ispositioned within a chamber port.

The air segment or bubble detector has a detector body with aflow-through passage in the body through which the sample and variousfluid reagents flow. There is a transverse passageway in the body whichintersects the flow-through passage. A fiber optic is positioned in thetransverse passageway intersecting the flow-through passageway. Thefiber optic has a passageway which communicates with the flow-throughpassageway in the body and forms a continuous part thereof. A lightsource is positioned at one end of the transverse passageway alignedwith the fiber optic to project light through the fiber optic. A lightdetector in the body is positioned transversely of the fiber optic andthe flow-through passageway. By this mechanism, when two fluids or afluid and air having different indices of refraction pass consecutivelythrough the fluid passageway in the fiber optic, a change in the amountof light reflected from the fiber optic is detected by the lightdetector. A pump is employed for pumping a sample in series through theprobe, the bubble or air segment detector, the ion selective electrodes,the reference membrane, and thence to a waste disposal chamber.

Electronic means are employed for measuring the voltage signal generatedbetween the ion selective electrode and the reference electrode forcalculating the ionic value of the electrolyte being measured.

The waste disposal chamber is located in a reagent pack which contains apair of relatively flat, flexible pouches with sealed perimeters. Thepouches are substantially equal size in volume and each pouch has aplurality of separate sealed compartments. One compartment is for thedisposal waste, and the other compartments contain various fluidreagents and a wash solution.

A fitment is sealed to each pouch. The pouches are disposed in a sealedreagent pack with their perimeters and the fitments in juxtaposition. Atube which is in fluid communication with each compartment projects fromthe juxtaposition fitments outwardly of the pack. The centers of thetubes are arranged as the corners of a parallelogram.

Each chamber port in the slide valve communicates via a passageway withan opening in the face of the slide valve. The center of the openings inthe slide valve and the tubes projecting from the reagent pack arearranged as the corners of a parallelogram of equal size to permit thetubes to mate with the openings in the slide valve in fluidcommunication.

A check valve is located in each passageway between the chamber portsand the openings in the face of the slide valve.

The above and other features of the invention including various noveldetails of construction and combinations of parts will now be moreparticularly described with reference to the accompanying drawings andpointed out in the claims. It will be understood that the particularelectrolyte analyzer embodying the invention is shown by way ofillustration only and not as a limitation of the invention. Theprinciples and features of this invention may be employed in varied andnumerous embodiments without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of an electrolyte analyzer embodying featuresof the present invention.

FIG. 2 is a front elevation of the analyzer.

FIG. 3 is a rear elevation of the analyzer with parts broken away.

FIG. 4 is a front view of a cam employed in the analyzer.

FIG. 5 is a rear view of cam of FIG. 4.

FIG. 6 is a side elevation, partly in section of a slide valve employedin the analyzer.

FIG. 7 is a sectional view taken on the line VII--VII on FIG. 6.

FIG. 8 is a detail view of interlocking fitments of the reagents andwaste disposal pouches.

FIG. 9 is a rear elevation of the reagent pack employed in the analyzer.

FIG. 10 is a front elevation of the reagent pack.

FIG. 11 is a front elevation of the reagent pouch.

FIG. 12 is a front elevation of the waste disposal pouch.

FIG. 13 is a sectional view of the bubble detector taken on the lineXIII--XIII of FIG. 15.

FIG. 14 is an exploded rear elevation of a reservoir housing and areference membrane contained therein.

FIG. 15 is an exploded front elevation of the reservoir housing and theelectrodes and bubble detector contained therein.

FIG. 16 is an exploded bottom view of the reservoir housing and thereference electrode contained therein.

FIG. 17 is a component block diagram.

FIG. 18 is an exploded view of the drive assembly of the analyzer.

FIG. 19 is a rear perspective view of the reagent pack.

FIG. 20 is a perspective view, on enlarged scale, of the fitments of thereagent pack.

BEST MODE OF CARRYING OUT THE INVENTION General Organization

The invention is embodied in a stat electrolyte analyzer for measuringelectrolytes in solution. In general, the analyzer has ion selectiveelectrodes 97, 98 (FIGS. 15 and 17) for sensing elements; a bubbledetector 300 (FIGS. 2, 13, and 15) for sensing air bubbles or segmentsof air; a sampling probe 70 (FIGS. 1 and 2) for aspirating fluid samplesor reagents; a peristaltic pump 55 (FIGS. 1, 2, and 18) for moving fluidsamples, reagents and air segments through the sampling probe 70,thence, past the bubble detector 300 and electrodes 97, 98, and into awaste disposal pouch 32 (FIG. 12); a DC motor 18 and two way clutch 17(FIG. 18) for driving the peristaltic pump 55 and a cam 14 which, inturn, operates the sampling probe 70 via two linking arms 7 and 12;operational amplifiers 194 and 195 (FIG. 17) for buffering the voltagesignals generated by the ion selective electrodes 97, 98; an analogmultiplexer 191 for selecting signals; an A to D converter 189 forconverting the signals into the digital domain; a microprocessor basedcomputer 190 for controlling the mechanical functions of the analyzerand for computing the activity of the electrolyte to be measured; adigital display 188 for showing results and displaying messages andquestions; reagent pouches 30 and 32 (FIGS. 11 and 12) containingstandard solutions for calibrating the electrodes; reagent pouch 31containing maintenance solution; a waste disposal pouch 30 for spentsample and reagent solutions; a reagent pack 20, 21 containing thepouches; a slide valve 64, which serves as an interface between thereagent pack and sample probe; and an analyzer housing 100 in which allthe aforesaid components are assembled.

The Analyzing and Detecting Elements

There will be seen in FIGS. 2 and 15, the flow-through bubble detector300, the flow-through potassium ion-selective electrode 98 which has amembrane containing valinomycin, and the flow-through glass sodiumelectrode 97. A flow-through reference membrane assembly 96, and asilver/silver chloride reference electrode 95 are seen in FIG. 14.

A flow-through tube 299 (FIG. 15) of the bubble detector 300 isconnected via flexible coupling 298 to the flow-through tube 94 of thepotassium electrode 98 which, in turn, is connected via flexiblecoupling 93 to the flow-through tube 92 of sodium electrode 97 which, inturn, is connected via flexible coupling 91 to the flow-through tube 90(FIG. 14) in the reference membrane assembly 96.

The potassium and sodium electrodes 99, 97 are mounted in a guide track89 (FIG. 14) of a detachable reservoir housing 88. The electrical pins86, 87 of the potassium and sodium electrodes 97, 98 are perpendicularto the cylindrical axis of the guide track 89 and the flow-through tubes92, 94 of the electrodes 97, 98. They extend beyond the backside of thereservoir housing 88 and plug into electrical jacks 84, 85 (FIG. 3) inthe analyzer housing 100. As such, the pins 86, 87 and electrodes 97, 98help support the reservoir housing 88.

The bubble detector 300 is also mounted in the guide track 89, and plugsinto an electrical connector 205 (FIG. 3) which also serves to supportthe reservoir housing 88. The bubble detector 300 is at the top of theguide track 89, and close to the top of the reservoir housing 88. Thepotassium electrode 98 is below the bubble detector 300, and the sodiumelectrode 97 rests in the bottom of the guide track 89.

The Reference Membrane Assembly

The reference membrane assembly 96 (best seen in FIG. 14) is cylindricaland fits into a cylindrical cavity 83 (FIG. 15) in the bottom of thereservoir housing 88. It is held in place by O-rings 81, 82 positionednear each of its ends. They form a watertight fit with the cylindricalcavity 83. The cylindrical axis of cavity 83 is aligned with the axis ofthe flow-through tubes 94, 92 of the potassium and sodium electrodes 98,97. The reference membrane 96 assembly has a flow-through tube 80, thecenter section of which is of V shape and extends to the outercylindrical wall of the assembly. Its upper end is connectable with thelower end of the flow-through tube 92 of the sodium electrode 97 viacoupling 91 (FIG. 15). A portion of the cylindrical wall of the assemblyis cut away where it is intersected by the V shaped portion of theflow-through tube 80. A cellophane membrane 79 is secured to the outsidecylindrical wall of the reference membrane assembly 96 and covers theopening in the outside wall where it is intersected by the V shapedportion of the flowthrough tube 80. The diameter of that portion of thereference membrane assembly 96 between its ends and containing thecellophane membrane 79 is less than the diameter of the cavity 83 sothat the cellophane membrane 79 is not damaged when replacementreference membrane assemblies 96 are installed in the reservoir housing88.

The cylindrical cavity 83 (FIG. 15) into which the reference membrane 96fits is connected by means of an open portion 78 to a reservoir cavity77 in the reservoir housing 88. It contains a 2 molar KCl referencesolution, whereby the cellophane membrane 79 is surrounded by thereference solution. The pressure created by the head of referencesolution assures a positive flow of that solution through the cellophanemembrane 79 whereby contamination and clogging of the membrane 79 by thesample solution is reduced. The reference membrane assembly 96 ispositioned farthest from the potassium electrode 98 to prevent possiblecontamination of the valinomycin membrane by the reference solution.

The Reference Electrode

The reference electrode 95 (FIG. 16) is a silver/silver chloridereference electrode. It contains an internal KCl filling solution and aceramic frit 74. The reference electrode 95 is secured in a cylindricalcavity 73 in the backside of reservoir housing 88 by screw threads onits outer end. The cylindrical cavity 73 communicates with the reservoircavity 77. The inner end of reference electrode 95 has an O-ring sealwhich forms a water tight fit with the cylindrical wall of cavity 73and, as such, forms a seal with respect to the reference solutioncontained in reservoir cavity 77. This end also contains the ceramicfrit 74 which is exposed to the reference solution 76 whereby anelectrical connection is completed between the sample solution passingthrough the reference membrane assembly 96, the reference solution andthe reference electrode 95.

The reference electrode 95 has an electrical pin 72 which extends beyondthe backside of the reservoir housing 88 and which fits into electricaljack 71 (FIG. 3) in the analyzer housing 100. It serves as the principalsupport to the reservoir housing 88 which can be installed or removedfrom the analyzer housing 100 by simply plugging or unplugging pins 86,87, and 72. The concentration of the KCl reference solution 75 in thereference electrode 95 is 2 molar KCl to minimize the liquid junctionpotential.

The Bubble Detector

The f1ow-through air segment or bubble detector 300 is illustrated indetail in FIG. 13. The body 297 of the detector 300 contains ahorizontal cylindrical cavity 296 which passes through, and isperpendicular to, the vertical cylindrical axis of the detector body297. Disposed in one end of the cavity 296 is a LED light source 295. Afiber optic 294 is disposed in the center section of the cavity 296. Thefiber optic 294 has a diameter of about 0.125 inches and it is cementedin the cavity 296. Light from the LED 295 passes through the fiber optic294 and out the opposite end of cavity 296. Perpendicular to cavity 296is a horizontal cylindrical cavity 293 having a diameter of about 0.20in. and which intersects, and ends at, the center section of cavity 296.Disposed in the outer end of cavity 293 is light detector 292.

The flow-through tube 299 of the detector 300 is comprised of a verticalcylindrical cavity passing through the vertical center axis of body 297.It is perpendicular to, and passes through, the fiber optic 294. Thediameter of the cavity is about 0.030 in. The operation of the bubbledetector will be described in greater detail hereinafter.

The Sample Probe

The upper end of the tubular sample probe 70 is attached to a probeguide arm 68 (FIG. 1). The middle and lower end of probe 70 passthrough, and are guided by a slide valve 64. The sample probe 70 has anoutside diameter of 0.049 in. and an inside diameter of 0.034 in. Theprobe 70 also has a side port 63 which is located 1/4 in. from itsbottom end and has a diameter of approximately 0.031 in. The lower endof the probe is closed by a solid plug. The sampling port 63 interfaceswith the ports in the slide valve 64 as will be more fully describedhereinafter.

The upper end of probe 70 is connected to the bubble detector 300 byflexible tubing 60 having an inside diameter of 0.039 in. The length ofthe tubing 60 is about 61/4 in. and flexes sufficiently to permit theprobe 70 to travel up and down through the slide valve 64. As notedabove, the flowthrough tubes 299, 94, 92, and 90 of the bubble detector300, potassium electrode 98, sodium electrode 97, and the referencemembrane assembly 96, respectively, are connected together by flexiblecouplings 298, 93, and 91, so that a continuous fluid path is formedfrom sampling port 63 in the probe 70 through the reference membraneassembly 96. The total volumetric displacement of the fluid path fromport 63 of probe 70 to the bottom of the reference membrane assembly 96is approximately 250 microliters.

The Peristaltic Pump

Flexible tubing 59 (FIG. 1) is connected to the bottom end of thereference membrane assembly 96, and passes tightly around rollers 56 ofperistaltic pump 55 to a male fitting 207 on the slide valve 64. Thetubing 59 has an inside diameter of 0.081 in. and is attached to theanalyzer housing 100 at two points 57, 58 before and after the tubing 59passes around the pump 55 so that the form of tubing 59 around the pump55 is U-shaped and contacts approximately 180 degrees of the pump 55.When the pump 55 is rotated, the tubing 59 is compressed by the pumprollers 56. The point of compression travels in the direction ofrotation of the pump 55 and at the speed of rotation of the pump 55.Fluid or air contained in the tube 59 is displaced ahead of the point ofcompression and a vacuum is created in the tube 59 behind the point ofcompression.

The Slide Valve

The slide valve 64 is best seen in FIGS. 6 and 7. It has a verticalcylindrical cavity 53 having a diameter of 0.062 in. and through whichthe probe 70 reciprocates. The cylindrical cavity 53 contains fourchamber ports 49, 50, 51, and 52 which are equally spaced apart. Theupper three ports 50, 51, and 52 communicate with three parallelchannels, 46, 47, 48, which are perpendicular to the vertical axis ofcavity 53. The channels 46, 47, 48, terminate at openings 40a, 40b, and40c on one face 149 of the slide valve 64 which will be described ingreater detail hereafter.

Port 49 is vented to atmosphere by opening 148. The chamber ports 49,50, 51, 52 are approximately 0.062 in. in diameter and 0.18 in. inlength. They are approximately 0.250 in. from each other. Neck portions206 are located between the ports and have radii of 0.018 in. The crosssection at the narrowest point of the cavity 53 is about 0.038 in.

The slide valve 64 is made of elastomeric material such as rubber,butyl, or silicones whereby the sections 206 of the cylindrical cavity53 between chamber ports 49, 50, 51, 52 squeeze the probe 70 as itpasses through them so that an air and liquid tight seal is formedbetween the chamber ports 49, 50, 51, and 52 and the probe 70. Thenecked portions 206 thus function as O-rings. Since the distance betweencenters of the chamber ports is 0.25 in. and since the side port 63 ofprobe 70 is approximately 1/4 in. from its bottom end 65, each of thechamber ports 49, 50, 51, and 52 is sealed from the others when sideport 63 of the probe 70 is aligned with one of the ports 49, 50, 51, and52.

Each of the three channels 46, 47, 48 contains a duck bill type checkvalve 44. The valves are made of soft rubber. They are cylindrical nearone end with a cylindrical ring 61 at the end, and are tapered to a fineslit 42 on the other end. Each of the channels 46, 47, 48 has acylindrical slot into which the cylindrical ring 61 seats and wherebythe check valve 44 is held in place in the channel. Air or liquidentering the cylindrical end, i.e. from left to right as seen in FIG. 6expands the tapered end 42 such that the flow opens the slit 42 wherebythe air or solution passes through the check valve 44. On the otherhand, fluid going in the opposite direction tends to compress thetapered end and hence, the fine slit 42, whereby no fluid passes throughthe valve 44 in that opposite direction.

The slide valve 64 also contains a V shaped channel 202 which has themale fitting 207 at one end onto which tubing 59 connects (see FIG. 2).Tubing 59 communicates with the flow-through tube of the referencemembrane assembly 96. Channel 202 terminates in an opening 201 on thesame face 149 as openings 40a, 40b, and 40c. These openings are arrangedin a predetermined geometric pattern.

It will be seen in FIG. 6 that the openings 40a and 40c in the slidevalve 64 are in vertical alignment. The openings 201 and 40b are also invertical alignment but spaced laterally from the openings 40a and 40b.The openings 201 and 40b are located higher on the slide valve 64 thanthe openings 40a and 40c, respectively. The centers are thus located atthe corners of a parallelogram. A parallelogram is shown forillustrative purposes. Other predetermined geometric patterns may alsobe employed.

The openings 40a, 40b, 40c, and 201 function as receptacles to wedgeshaped fitments 38 and 39 (FIGS. 8 and 12 and 20) which act as aninterface between the slide valve 64 and the reagent pack 26. Thefitments 38 and 39, each have two rigid tubes passing through themdesignated 37, 37a, 37b, and 37c. One end of each tube fits intoopenings 40a, 40b, 40c, and the opening 201 in slide valve 64 as isexplained more fully below. There is a slight shoulder or barb (FIG. 20)near the end of each tube 37 which causes a water tight fit when thetube 37 is pushed into the openings in the slide valve 64. The centersof tubes 37, 37a, 37b, and 37c projecting from the reagent pack are alsoarranged in a geometric pattern of the same size and slopes as theopenings in the slide valve (See FIGS. 19 and 20). The dimensions of theparallelograms are identical to assure that the tubes 37, 37a, 37b, and37c fit into the openings 201, 40a, 40b, and 40c respectively.

Reagent Pouches

The other end of the tubes 37 fit into f1exible tubes 34, which aredisposed in reagent pouches 32 and 33 (see FIGS. 11 and 12). Each pouch32, 33 is made of two equal substantially rectangular, flat pieces offoil laminate which are heat sealed together at their perimeters torender them hermetically and fluid tight. Each pouch, 32, 33 has twocompartments which are also formed by heat sealing a dividing linebetween them. The pouches 32, 33 being made out of foil, preventevaporation of the reagents contained therein. In pouch 33, onecompartment 145 has a capacity of about 130 ml and intended to containStandard B, and a second compartment 146 is intended to contain about400 ml of Standard A. In pouch 32, there is one small compartment 31which can contain about 15 ml of daily wash or maintenance solution. Theremainder 30 of pouch 32 serves as a waste disposal compartment forreceiving spent sample solutions and reagents.

Each pouch 33, 32 has an opening 33a and 32a which is sealed to thewedge surfaces 38a and 39a of the fitments 39, 38 to form a permanentair tight seal between the pouches 33, 32 and the fitments 38, 39. Eachflexible tube 34 is also sealed from the other, and each compartment ina pouch is sealed from the other compartment. The flexible tubes 34 runto the bottom of each pouch compartment to insure accessibility to allof the reagents contained therein. In the case of the waste disposalcompartment 30, the tube 34 need only be of sufficient length to connectto the top of the compartment 30.

Reagent Pack

Each fitment 38, 39 has interlocking fingers 38b and 39b to enable thefitments to be snapped together and held in place as an integral part.The reagent pouches 32, 33 are of substantially the same size and havesubstantially the same internal volume are joined by the fitments 38,39, lie side by side in parallel and are contained in the rectangularreagent pack 26.

The reagent pack 26, shown in FIGS. 9, 10, and 19 is made of two highimpact polystyrene halves, 20, 21. The back half 20 is contoured in apattern that mates with contours of the analyzer housing 100 andperistaltic pump 55 which project outwardly through the front side ofthe analyzer housing 100 as seen in FIG. 1. The front half 21 of thepack has a flat surface which is flush with the analyzer housing 100when the pack is in place. The perimeters of the pack halves 21, 20match and contain slot receptacles 24, 25 which engage the fitments 38,39 and hold them in place. The perimeters of the pack halves 20, 21 arebonded together to form a permanent closure.

The reagent pouches 32, 33 are secured inside the reagent pack 26 by asupport post 19 projecting inwardly from in the back pouch half, 21. Ahole 22 in the sealed perimeter trim of each pouch half 20, 21 is placedover the support post 19 and supported thereby. There is an inwardlyprojecting tapered indentation 54 in the front pack half 20 which mateswith the support post 19. A conical indentation 54a in the outer surfaceserves as a finger hold for gripping the reagent pack 26 when theoperator installs it into the analyzer by plugging the fitments 38, 39into receptacles 40, 40a, 40b, and 201, of slide valve 64. The bottom ofthe reagent pack 26 is supported by the analyzer housing 100.

The Peristaltic Pump and Drive Mechanism

Peristaltic pump 55 is driven by a 24 volt D.C. gear motor 18. The pump55 is mounted on the front half of a two-way cylindrical clutch 17 (FIG.18) which is mounted on the output shaft 16 of the D.C. gear motor 18.The pump housing 23 is surrounded by a pump shield 15 (FIG. 2) which ismounted in the analyzer housing 100 by means of a snap fit. The shieldis made of elastomeric material and fits snugly against the pump housing23. It acts as a brake to prevent backturning of the pump when the backhalf of the two-way clutch 17 is rotating in the opposite direction.

A cam 14 (shown in detail in FIGS. 4 and 5) is mounted on the back halfof the two-way clutch 17 and rotates in the opposite direction to theperistaltic pump 55. The cam has a continuous groove or slot 13 on itscircular disc face which varies in distance from the center of the camas a function of the angle of rotation over 360 degrees. The cam 14drives a front link arm 12 (seen best in FIGS. 1, 2, and 3). It isapproximately 4.2 in. in length. One end of link arm 12 is attached by apivot joint 10 to analyzer housing 100 about which it is free to rotate.The link arm 12 has a cam follower pin 11 intermediate of its ends andwhich is located about 1.9 inches from the pivot point 10. The diameterof the pin 11 is just slightly less than the width of slot 13, which isabout 0.13 in. The other end of link arm 12 is attached by a pivot joint9 to one end of a second link arm 7. The opposite end of the second linkarm 7 is attached to the probe guide arm 68 by pivot joint 6. The probearm 68 is constrained to move vertically by a vertical rod 5 whichpasses through a hole in probe arm 68. Rod 5 is attached to the analyzerhousing 100 at both of its ends. The displacement of the probe guide arm68 is equal to the vertical displacement of cam follower pin 11 timesthe distance between pivot point 10 and pivot point 9, divided by thedistance between pivot point 10 and cam follower pin 11. As the cam 14is rotated by the DC motor 18, the probe arm 68 glides up and downvertical rod 5, and hence probe 70 is also displaced vertically.

Operation of the Cam-driven Probe

The slot 13 in cam 14 is divided into 9 segments 215 to 223 (FIG. 4), aportion of each of which has a constant radius. These portionscorrespond to 9 positions of the probe 70 which are sequenced in theorder set forth in Table No. 1 together with a description of thecorresponding function performed by the analyzer at each position:

                  TABLE 1                                                         ______________________________________                                        Position of Cam 14                                                                            Description of Function                                       ______________________________________                                        215             215                                                           Probe 70 in lowest chamber                                                                    Pump 55 aspirates air                                         port 49 of slide valve 64                                                                     through channel 148 in                                                        slide valve 64                                                216             216                                                           Probe 70 in next to                                                                           Pump 55 aspirates STD "B"                                     lowest chamber port 50                                                                        from compartment 145                                          of slide valve 64                                                                             of pouch 33                                                   217             217                                                           Probe 70 in next to                                                                           Pump 55 aspirates daily                                       highest chamber port 51                                                                       wash solution from compartment                                of slide valve 64                                                                             31 of pouch 32                                                218             218                                                           Probe 70 in highest                                                                           Pump 55 aspirates Standard                                    highest chamber port 52                                                                       "A" from the compartment 146 of                               of slide valve 64                                                                             pouch 33                                                      219             219                                                           Probe 70 in next to                                                                           Pump 55 aspirates daily                                       highest chamber port 51 of                                                                    wash solution from compartment                                slide valve 64  31 of pouch 32                                                220             220                                                           Probe 70 in next to                                                                           Pump 55 aspirates Standard "B"                                lowest chamber port 50 in                                                                     from compartment 145 of                                       slide valve 64  pouch 33                                                      221             221                                                           Probe 70 in lowest chamber                                                                    Pump 55 aspirates air                                         port 49 of slide valve 64                                                                     through channel 148 in                                                        slide valve 64                                                222             222                                                           Probe 70 about 4" below                                                                       Pump 55 aspirates sample                                      slide valve 64  solution from a deep                                                          container e.g. a vacutainer                                   223             223                                                           Probe 70 about 1" from                                                                        Pump 55 aspirates sample                                      bottom of slide valve                                                                         solution from a short container                               64              or large syringe                                              ______________________________________                                    

The total distance travelled by probe 70 is approximately 5 inches whichcorresponds to 2 inches of vertical travel by cam follower pin 11.

The cam drive assembly of the analyzer is illustrated in the explodedview of FIG. 18. The D.C. motor 18 is mounted on a rectangular plate 198(FIG. 3). Its output shaft 16 passes through a hole 144 in the mountingplate 198 and is perpendicular to the mounting plate 198. The clutch 17,cam 14, and pump 55 are all on the opposite side of the mounting plate198 from the D.C. motor 18. The mounting plate is bolted to the insideof the front half of the analyzer housing 100 which contains a holethrough which pump 55 protrudes. The cam 14 is parallel to the mountingplate 198.

There are three rubber fingers 131 (FIG. 1) which are mounted on plate198 and are disposed in between the cam 14 and mounting plate 198. Theyexert a slight pressure on cam 14 in the event cam 14 attempts to movebackwards.

The motor 18 has an approximate 127 to 1 reduction ratio such that thecam 14 or pump 55 on the outout shaft 16 makes 1 turn for every 127turns of the motor shaft 1. The motor shaft 1 has a slotted wheel 200(FIG. 3) on its end which passes through an optical interrupter 199mounted on frame assembly 2, which is also attached to the mountingplate 198. The wheel 200 contains 8 segments. The interrupter 199 keepscount of the revolutions of the motor 18. A second optical interrupter197 is mounted on plate 198 which detects nine slits 186 (FIG. 5) on theback side of the cam 14 corresponding to the beginning of each portionof each of the nine segments which has a constant radius. The portion ofeach segment having a constant radius corresponds to about 3 revolutionsof DC motor 18. The slits 186 operate as reference points to the ninesegments as is more fully explained below.

The Electronic Control Mechanism

The computing functions of the analyzer are performed by amicroprocessor based computer and other electronic components which arecontained on a circuit board 196 (FIG. 1) which is mounted in the fronthalf of analyzer housing 100. The computer and other electroniccomponents, are powered by a power supply (not shown) in the back halfof analyzer housing 100. These components are illustrated by a blockdiagram in FIG. 17. The electrodes, 95, 97, 98, give rise to a voltagesignal when a sample solution or Standard A or B passes through theirflow-through tubes. The signal is related to the activity of thepotassium and sodium ions in the sample solution or reagents inaccordance with the well known Nernst equation. The voltage signals areintroduced into operational amplifiers 194, 195 which buffer the signal.The operational amplifiers 194, 195 have a high input impedance incomparison to the electrodes 95, 97, 98 in order to prevent too muchcurrent from being drawn through the electrodes, 95, 97, 98.

The output from the operational amplifiers 194, 195 is introduced intoanalog multiplexer 191. Upon receiving a programmed command from thecomputer 190, the multiplexer will select the output of one of theoperational amplifiers 194, 195 and transmit this to A/D converter 189.The A/D converter 189 takes the analog signal which it receives andconverts the difference between it and the output signal of thereference electrode 95 into a digital signal which in turn istransmitted to the computer 190. The sequencing operation of the A/Dconverter 189 is also controlled by the computer 190. The computer 190determines the value of the activity of potassium and sodium ions inaccordance with the Nernst equation as is explained more fully below.The results are exhibited within 60 seconds on a liquid crystal display188.

The computer 190 also controls the mechanical functions of the analyzer.It sends signals to the solid state motor driver 187 which in turndrives D.C. motor 18. The motor driver 187 can send four signals to theD.C. motor: (1) motor forward; (2) motor reverse; (3) motor coast; (4)motor brake. The torque of the D.C. motor 18 in the motor forward orreverse modes is controlled by the number and width of the pulsesoutputed by the motor driver 187 pursuant to the input commands of thecomputer 190.

The computer 190 receives inputs from the optical interrupters 199 and197. Optical interrupter 199 sends eight pulses for one revolution ofslotted wheel 200 and hence motor shaft 1. As such, it acts as atachometer measuring the number of revolutions of DC motor 18 to 1/8revolutions. Optical interrupter 197 sends a pulse signal to computer190 every time it senses one of the slits 186 in rim 141 correspondingto the nine positions of cam 14.

When the computer 190 is driving the D.C. motor 18, it sends a signal tomotor driver 187 to go in the forward or reverse directions, and when itwants to stop the motor 18, it commands the motor driver 187 to go intothe motor brake mode. For example, if the probe 70 is to go from port 50of slide valve 64 to port 51 of slide valve 64 (i.e. from position No.216 to position No. 217, on cam 14) the computer 190 will command themotor driver 187 to go into the forward mode. At the same time, thecomputer commences counting the number of pulses it receives fromoptical interrupter 199, and hence the number of revolutions of motorshaft 1. As the slit 186 in rim 141 corresponding to position No. 217passes through optical interrupter 197, this information is received bythe computer 190 which simultaneously reads the tachometer 199 andcommands the motor driver 187 to go into the brake mode. It compares thetachometer 199 reading with the preset number of revolutionscorresponding between position No. 216 and 217, and if the difference isgreater than a set tolerance, it computes the actual cam position andcontinues rotating until the real position 217 is reached.

When the computer drives the peristaltic pump 55, it sends a command tomotor driver 187 to go into the motor reverse mode. When the motor 18starts, the computer commences counting pulses from optical interrupter199, and hence, the number of revolutions of motor shaft 1, and comparesthis information against a preset number of revolutions (correctedperiodically for pump tubing stretch) corresponding to the mechanicalfunction to be performed. For instance, when the pump 55 is to aspirate100 microliters of sample solution, the pump 55 must make about 2revolutions. When the preset number of revolutions is reached, thecomputer 190 signals the motor driver 187 to go into the motor brakemode.

The pumping rate, i.e. the number of microliters per revolution of pump55, or output shaft 16 of motor 18, changes from time to time as thetubing 59 stretches with use and time. The rate is checked periodicallyby the computer 190 and updated to compensate for changes in the pumptubing 59. The computer 190 utilizes inputs from the bubble detector 300in the correction procedure.

The bubble detector 300 operates as follows. Light from LED 295 (FIG.13) passes through fiber optic 294 and out the end of cavity 296. When asample solution or reagent passes through the flow-through tube 299including that section 291 passing through the fiber optic 294, there islittle or no change in the path of the light as the index of refractionof the fiber optic 294, about 1.4, is close to the index of refractionof water, about 1.4. Hence, no light is deflected to light detector 292.However, when a bubble or segment of air having an index of refractionof about 1.0 passes through the fiber optic 294, a significant amount oflight is reflected. Some of this light is perpendicular to the axis ofthe fiber optic 294, and hence passes out the side of the fiber optic294. It is sensed by the photo diode light detector 292. The outputsignal is introduced into an operational amplifier (not shown) whichconverts the low level current to a high level voltage signal. Theoperational amplifier also controls the LED 295 current.

The output of the operational amplifier is introduced into adifferentiator (not shown) whose output operates an analog latch 142.Hence, upon the passing of an air bubble or segment, the latch 142 istripped. It is reset each time it is read by the computer 190. Theoutput of the detector 300 is also introduced into A/D converter 183which in turn is introduced into computer 190. Hence, if at any time thecomputer reads the A/D converter 183, it will know whether an air bubbleor segment is being detected by detector 300.

In the pump tube calibration procedure referred to above, the pump 55aspirates an arbitrary volume of fluid. It then aspirates a segment ofair. The computer 190 then commands the motor driver 187 to go into themotor reverse mode for the number of revolutions necessary to positionthe fluid such that the end of the fluid will be located at the fiberoptic 294 of bubble detector 300. At the same time, the computer 190looks for the segment of air following the fluid by monitoring latch 142or A/D convertor 183. If the air segment is not detected, the computer190 drives the pump 55 until the air segment is detected by the bubbledetector 300. The computer 190 then compares the difference, and updatesthe pumping rate.

The programs for operating the analyzer are stored in the EPROMs of thecomputer 190. There are four operational modes; ANALYZE BLOOD?; ANALYZEURINE?; SEE LAST RESULTS?; and MAINTENANCE? Each of these modes can beselected by the operator's pressing a red (no) button 178 on theanalyzer (FIG. 1) until the desired mode appears on display 188. Whenthe desired mode appears, the operator presses a green (go) button 178.Thereafter, the operator is prompted through steps by questions andmessages appearing on the display 188.

A typical cycle is illustrated by the "analyze blood" mode. Standard Ais already in the fluid path. The probe 170 is positioned at the highestchamber port 52 of slide valve 64. When the operator presses the go(yes) button 178 to the question "ANALYZE BLOOD?" on the display 188,the probe 70 moves to the lowest chamber port 49 of slide valve 64 andaspirates about 20 microliters of air. The probe 70 then goes to about4" below slide valve 64 and the question, "PROBE IN BLOOD?" appears ondisplay 188. If the sample is in a container such as a large syringe,the operator will press the red (no) button 179 and the probe 70 willautomatically go to the other sample position, 1 inch below slide valve64.

After the probe is in the blood sample, the operator presses the green(yes) button 179, and the pump aspirates about 100 microliters ofsample. The probe 70 then moves to the lowest chamber port 49 and thepump 55 aspirates about 20 microliters of air. Next, the probe 70 movesto the highest chamber port 52 and pump 55 aspirates enough Standard A(about 80 microliters) to position the sample of blood such that thetrailing end of the sample is located in bubble detector 300. Thecomputer 190 then takes reading from the electrodes 95, 97, 98.Thereafter, more Standard A is aspirated by pump 55 until a sufficientamount rinses the electrodes 95, 97, 98. The computer 190 then takeselectrode readings of Standard A and compares this with its reading ofStandard A prior to the cycle. If the difference is within a toleranceamount, the computer 190 sends the results of the analysis to display188.

The computer 190 makes its calculations by comparing the potentialmeasured in the sample with the potential measured in Standard A. Giventhe slope of the electrode, and concentration of Standard A, thecomputer can determine the concentration of potassium and sodium in thesample solution in accordance with the Nernst equation and an empiricalcorrection curve. The slope is previously determined by the computer 190during a calibration cycle by subtracting the potentials measured fromStandard A and Standard B, the concentrations of which are both known.This calculation is performed automatically every two hours when theanalyzer is in the operational mode. If the slope falls outside apredetermined range, the computer 190 sends a message to the operatorvia display 188 that the electrodes need replacing.

Maintenance functions are also programmed into the computer 190. Forinstance, 300 ul of daily wash solution from compartment 31 of pouch 32are pumped through the system once per day to rinse and condition thesodium electrode 97. The computer 190 sends periodic maintenancemessages to display 188 telling the operator when it is time to changethe reagent pack 26, the electrodes, 95, 97, 98 reference membraneassembly 96, and pump tubing 59.

The present invention is not limited to the disclosed embodiment, butincludes other embodiments which will occur to those skilled in the art.For instance, electrodes which sense bicarbonate, pH, lithium, calciumor other ions may be utilized in lieu of the potassium and sodiumelectrodes 97, 98. More than two electrodes may also be utilized in theanalyzer. The inside diameters of the flow-through tubes of the bubbledetector 300, potassium and sodium electrodes 97, 98 or the fluid pathelements such as the sampling probe 70, the fluid path tubing 60, andpump tubing 59 may be varied depending upon the application. In thespecific embodiment set forth, the inside diameters were chosen toaccommodate a 100 microliter sample size of blood, serum, or plasma. Theradius of the necked sections 206 of the cylindrical cavity 53 in slidevalve 64 will vary depending upon the elasticity of the material ofwhich the slide valve 64 is constructed. Elastomeric "O" rings may alsobe employed in lieu of the necked portions 206. The material of theslide valve itself will depend on its compatibility with the reagentsand samples. Similarly, the interior dimensions and materials of thereagent pouches 32, 33 check valves 44, fitments 38, 39, tubes 37, andreagent pack 26 may vary upon the particular application.

The number of pouches, fitments, and number of chamber ports in theslide valve 64 may also be varied. Other motors with different reductionratios than DC motor 18 may also be utilized to drive the mechanicalcomponents. Similarly, variations to the cam slot 13, the mechanicallink arms 7, 12 and other physical arrangements are included herein.

With respect to the bubble detector 300, different light detectors, suchas photo transistors, may be utilized in lieu the photo diode 292 inwhich case the attendant operational amplifier may not be necessary. Theshape of the cavity 291 passing through the fiber optic 294 need not becylindrical. For example, a cavity formed as a right triangle might beused. In this case, light would be completely reflected off thehypotenuse when the cavity contains air. Other materials than the fiberoptic 294 may be used as the medium containing the cavity 291. What isessential is that the medium have an index of refraction sufficientlyclose to blood or water such that light will not be reflected when it isincident upon the cavity. Further, the detector 292 need not beperpendicular to the incident light depending upon the material that isused for the medium and the shape of the cavity that is utilized.

We claim:
 1. A fluid selecting system with a disposable reagent packcomprising:a. a fluid selector valve having a plurality of inputchannels arranged in a predetermined geometric pattern, an outputchannel and means for sequentially connecting any input channel to theoutput channel; b. a container pack containing a plurality of flexiblepouches for containing reagents, each pouch having an opening containinga fitment sealed to the pouch and in fluid communication with a reagentcontained in the pouch, the pouches being disposed in the reagent packwith their fitments in juxtaposition, the container pack having anopening in its perimeter containing and holding in place thejuxtapositioned fitments, the fitments each having a fluid connectorcompatible in size and engagable with an input channel in the selectorvalve, the connectors extending outwardly from the container pack andarranged in the same predetermined geometric pattern as the inputchannels in the selector valve, whereby the container pack can beplugged into, and unplugged from the selector valve so that each pouchin the reagent pack is in fluid communication with an input channel inthe selector valve.
 2. The reagent pack comprising:a. a container pack,and b. a plurality of flexible pouches for containing reagents, eachpouch having an opening containing a fitment sealed to the pouch and influid communication with the interior of the pouch, the pouches beingdisposed in the container pack with their fitments in juxtaposition, thecontainer pack having an opening in its perimeter containing means forholding in place the fitments, the fitments each having at least onefluid connector, the fluid connectors being arranged in a predeterminedgeometric pattern and maintained therein by the holding means in thecontainer pack to which, a fluid selector valve having compatible inputconnectors arranged in the same predetermined geometric pattern as thefluid connectors of the pack and connectible thereto may be, wherebyeach pouch in the reagent pack may be placed simultaneously in fluidcommunication with an input channel in the selector valve and wherebythe reagent pack may be plugged into or unplugged, from the selectorvalve as a unit.
 3. A reagent selecting system comprising:a. a tubularsampling probe having one end closed and a side port spaced a finitedistance from the closed end; b. a slide valve having a cylindricalpassageway through which the probe reciprocates, the passageway having aplurality of chamber ports each of which is sealed from the other portsby the sampling probe when the side port is positioned within a chamberport, a plurality of input channels, each chamber port communicating viaone of said impact channels with an opening on one face of thb slidevalve, the openings being arranged in a predetermined geometric pattern;and c. a container pack containing a plurality of flexible pouches forcontaining reagents, each pouch having an opening containing a fitmentsealed to the pouch and in fluid communication with a reagent containedin the pouch, the pouches being disposed in the reagent pack with theirfitments being in juxtaposition, the container pack having an opening inits perimeter containing means for holding in place the juxtapositionedfitments, the fitments each having a fluid connector compatible in sizeand engagable with the openings in the slide valve, the fluid connectorsextending outwardly from the container pack, and arranged in the samepredetermined geometric pattern as the openings in the slide valve,whereby the container pack can be plugged into, and unplugged from theslide valve so that each pouch in the reagent pack is in fluidcommunication with an input channel in the selector valve.
 4. A reagentselecting system according to claim 3 and further including means forsequentially aspirating and pumping reagents contained in the pouchesthrough the slide valve and probe.
 5. A reagent selecting systemaccording to claim 3 further including means for reciprocating thesample probe through the passageway in the slide valve, and forsequentially locating the sampling port in each chamber port in theslide valve and at a finite distance outside the slide valve to aspiratea sample solution from a sample container.